The present invention relates to cam phasers for reciprocating internal combustion engines for altering the phase relationship between valve motion and piston motion; more particularly, to cam phasers which are mountable on the front or forward ends of camshafts and which are supplied with pressurized engine oil from the camshaft oil supply; and most particularly, to an improved cam phaser assembly having an improved oil supply route through a camshaft.
Cam phasers are well known in the automotive art as elements of systems for reducing combustion formation of nitrogen oxides (NOX), reducing emission of unburned hydrocarbons, improving fuel economy, and improving engine torque at various speeds.
Typically, cam phasers employ a first element driven in fixed relationship to the crankshaft and a second element adjacent to the first element and mounted to the end of the camshaft in either the engine head or block.
In the known art, the first element is typically a cylindrical stator mounted coaxially to a crankshaft-driven gear or pulley and having a plurality of radially-disposed chambers and an axial bore, and the second element is a vaned rotor mounted to the end of the camshaft through the stator bore and having a vane disposed in each of the stator chambers such that limited relative rotational motion is possible between the stator and the rotor. The chambers are sealed typically by front and rear face seals of the stator. The camshaft and phaser are provided with suitable porting so that hydraulic fluid, for example, engine oil under engine oil pump pressure, can be brought to bear controllably on opposite sides of the vanes in the chambers. Control circuitry and valving, commonly a multiport spool valve, permits the programmable control of the volume of oil on opposite sides (C1 and C2) of each vane to cause a change in rotational phase between the stator and the rotor, in either the rotationally forward or backwards direction, thus advancing or retarding the timing of the valve opening and closing with respect to the pistons.
A serious problem is known in the art of manufacturing engines having cam phasers. Typically, the end portion of the camshaft which interfaces with the phaser requires substantial drilling and machining to provide hydraulic porting for the phaser. Specifically, in the prior art, the C1 oil gallery routing includes an annular groove in the camshaft at the cam bearing intersected by a plurality of bores drilled axially along the camshaft from the cam end. Another annular groove in the cam phaser intersects the bores to complete the routing. Drilling of the camshaft to provide the axially-directed bores is not easily and inexpensively performed, especially on chilled cast iron camshafts, because the bores are necessarily quite long and quite small in diameter. Further, being of small diameter, the bores can significantly reduce the pressure of oil being supplied to the cam phaser.
What is needed is an improved C1 oil gallery configuration in the camshaft that is easier and less expensive to manufacture and that improves the flow of oil to a cam phaser.
The present invention is directed to an improved configuration of the C1 oil gallery in a camshaft bolted to, and supplying oil to, a cam phaser. In the prior art, a first axial central bore in the camshaft is threaded over a portion of its outer end for receiving an axial bolt for securing a cam phaser to the camshaft. In the present invention, the axial bore is formed over a non-threaded outer portion at a diameter substantially greater than the diameter of the bolt. Upon assembly of the cam phaser to the camshaft, an annular, cylindrical gallery is formed between the bolt surface and the bore, which gallery replaces the plurality of axial bores required for the C1 gallery in the prior art. The prior art C2 gallery, which utilizes a second axial bore in the bolt itself, is substantially unchanged, and an O-ring around the cam bolt in the first axial bore seals the C1 and C2 pressure galleries from communicating with each other.